After you have added some copy to your blog post you may want to turn a word or words into a live link. You can do this by highlighting the words you want to become a link. While your words are still highlighted click on the third icon on the menu bar above where you type to post. When you hover over it a balloon that says "insert link" will appear. Click on it.
Below I want to turn the words Cutest Dog Ever.com into a link that takes viewers to my dog's website.
When you click on the "insert link" button the following window will open. it already has the "http://" in the window. Click on the blank space after and add in the rest of the url you want to link to. I've gone ahead and added in the url to my dog's website. The words you highlighted will automatically become a link.
This is what your new link will look like in the "Compose" mode of creating a post.